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है”ह”ह

IS 11918 (1987): Method for Determination of pH in Caseinsand Caseinates (Reference Method) [FAD 19: Dairy Productsand Equipment]

IS : 11918 - 1987 UDC 637.147.2 : 643’267’1 ( First Reprint NOVEMBER 1996) IS0 5546 - 1978

Indian Standard

METHOD FOR DETERMINATION OF JIH IN CASEINS AND CASEjlNATES ( REFERENCE METHOD )

[ IS0 Title : Caseins and Caseinates - Determination of PH ( Reference Method ) ]

National Foreword

This Indian Standard which is identical with IS0 5546 - 1978 ‘Caseins and caseinates - Determination of pH ( Reference method)‘, issued by the International Organization for Standardization ( IS0 ), was adopted by the Indian Standards Institution on the recommendation of the Dairy Products Sectional Committee and approval of the Agricultural and Food Products Division Council.

In the adopted standard, certain terminology and conventions are not identical with those used in Indian Standard; attention is particularly drawn to the following:

a) Wherever the words ‘International Standard’ appear, referring to this standard, they should be read as ‘Indian Standard’; and

b) Comma ( , ) has been used as decimal marker while in Indian Standards, the current practice is to use point ( . ) as the decimal marker.

Cross References

International Standard

ISO/R 707 ( IS0 707-1985 ) Milk and milk products - Methods of sampling

Corresponding Indian Standard

IS : 11546-l 985/lSO 707-1985 Methods of sampling of milk and milk products ( Identical )

ISO/ O/l Test sieves-Technical require- ments and testing - Part 1 Metal wire cloth

IS : 460 (Part 1) - 1985 Specification for test sieves : Part 1 Wire cloth test sieves ( third revision ) ( Technically equivalent )

For determining compliance with the test requirements prescribed in the standard, result of a test or analysis shall be rounded off in accordance with IS : 2-1960 ‘Rules for rounding off numerical values ( revised)‘.

Adopted 26 February 1987 I

8 August 1987, 61s I

or 2

BUREAU OF INDIAN STANDARDS MANAK BHAVAN. a ~AHAOUR SHAH ZAFAR MARG

NEW DELHI 110002

IS : 11918 - 1987 IS0 5546 - 1978

1 Scope and field of application

This International Standard specifies a reference method for

the determination of the pH of all types of casein [acid caseins

and rennet caseins) and of caseinates.

2 References

ISOIR 707, Milk and milk products - Sampling.

IS0 3310/l, Test sieves - Technical requirements and testing - Part 1 : Metal wire cloth.

3 Definition

pti of caseins and caseinatas : The pH, at 20 OC, of an aqueous extract of casein or an aqueous solution of caseinate, as determined by the procedure described in this International Standard.

4 Principle

Electrometric determination of the pH of an aqueous extract of casein or an aqueous solution of caseinate, using a pH meter.

6 Reagents

The reagents shall be of recognized analytical grade. Any water used in their preparation and the water used in the determination (8.2) shall be recently distilled water that has been protected from carbon dioxide absorption.

5.1 Buffer solutions, for calibration of the pH meter (6.2).

Two standard buffer solutions with pH values at. 20 OC which are known to the second decimal place and will bracket the pH value of the sample under test, for example phthalate buffer solution of pH approximately 4 and a borax buffer solution of pH approximately 9. In addition, a phosphate buffer solution of pH approximately 7 may be used.

6 Apparatus

6.1 Balance, accuracy 0.1 g.

6.2 pH meter, minimum sensitivity 0,05 pH unit, with a suitable glass electrode and a calomel or other reference electrode.

6.3 Thermometer, accuracy 0.5 “C.

6.4 Conical flask, capacity 100 ml, fitted with a ground

glass stopper.

6.5 Beaker, capacity 50 ml.

6.6 Grinding device, for grinding the laboratory sample, if necessary (see 8.1.41, without development of undue heat and without loss or absorption of moisture. A hammer-mill shall not be used.

6.7 Test sieve, wire cloth, diameter 200 mm, nominal size of

aperture 500 urn, with receiver, complying with IS0 3310/l.

6.8 Mixer.

6.9 Beaker, for the mixer (6.81, of at least 250 ml capacity.

7 Sampling

sea ISO/R 707.

6 Procedure

8.1 Preparation of the test sample

8.1.1 Thoroughly mix the laboratory sample by repeatedly

shaking and inverting the container (if necessary, after having

transferred all of the laboratory sample to an air-tight container

of sufficient capacity to allow this operation to be carried outi.

8.1.2 Transfer abou! 50 g of the thoroughly mixed laboratory

sample to the test sieve (6.7).

8.1.3 If the 50 g portion directly passes or almost completely

passes the sieve, use for the determination the sample as

prepared in 8.1.1

2

IS : 11918 - 1987 IS0 5546 - 1978

8.1.4 Otherwise, grind the 50 g portion, using the grinding device (6.6). until it passes the sieve. Immediately transfer all the sieved sample to an air-tight container of sufficient capacity and mix thoroughly by repeated shaking and inverting. During these operations, take precautions to avoid any change in the

water content of the product.

8.1.5 After the test sample has been prepared, the determina- tion (8.2) should be proceeded with as soon as possible.

8.2.3.2 Casainatas

Pour about 20 ml of the solution into the beaker (6.5) and im- mediatety determine the pH of this liquid, using the pH meter (6.2). after having rinsed the glass electrode carefulfy with water.

9 Expression of results

9.1 Recording of pH 8.2 Determination

9.1.1 Caseins 8.2.1 Calibration of pH meter

Adjust the temperature of the buffer solutions (5.1) to 20 T and calibrate the pH meter in accordance with the manufac-

turer’s instructions.

NOTES

1 The calibration should be carried out while the flasks are standing for 20 min (see 8.2.2.1 and 8.2.2.2).

2 If a series of samples is being tested, check the calibration of the pH meter with one or more of the standard buffer solutions at least every 30 min.

8.2.2 Preparation of test solution

8.2.2.1 Caseins

Weigh to the nearest 0,l g, into the conical flask (6.41, 5,0 g of the test sample (8.1), add 30 ml of water previously adjusted to

20 OC and stopper the flask. (If desired, 7.0 g of the test sample

and 42 ml of water can be taken.)

Shake the flask by hand for 10 s and allow to stand for 20 min

at about 20 OC.

8.2.2.2 Caseinates

Transfer to the beaker (6.9) 95 ml of water, add 5,0 g of the test

sample (8.11, and mix using the mixer (6.8) for 30 s.

Allow to stand for 20 min at abbut 20 ‘C

8.2.3 Measurement of pH

8.2.3.1 Caseins

Decant the supernatant ltquid into the beaker (6.5) and im-

mediately determine the pH of this liquid, using the pH meter

16.21, after having rinsed the glass electrode carefully with

water.

Record, as the pH of the aqueous extract of casein, the value read from the dial of the pH meter to at least one decimal place.

9.1.2 Caseinatea

Record, as the pH of the aqueous solution of caseinate, the value read from the dial of the pH meter to at least two decimal places.

9.2 Precision

9.2.1 Repeatability

The difference between two single results obtained on identical

test material by one analyst using the same apparatus within a

short time interval will exceed 0,l pH unit for casein extracts and 0.05 pH unit for caseinate solutions on average not more than once in 20 cases in the normal and correct operation of the

method.

9.2.2 Reproducibility

The difference between two single and independent results ob-

tained by two operators working in different laboratories on

identical test material will exceed 0.3 pH unit for casein extracts

and 0,15 pH unit for caseinate solutions on average not more

than once in 20 cases in the normal and correct operation of the

method.

10 Test report

The test report shall show the method used and the result ob-

tained, it shall also mention all operating conditions not

specified in this International Standard, or regarded as op-

tional, as well as any circumstances that may have influenced

the result.

The report shall include all details necessary for complete iden-

tification of the sample.

Reprography Unit, BIS, New Delhi, India 3